The present invention relates generally to particle blast systems, and is particularly directed to a device which provides improved introduction of particles into a transport gas flow for ultimate delivery as entrained particles to a workpiece or other target. The invention will be specifically disclosed in connection with a transport mechanism in a cryogenic particle blast system which introduces particles from a source of such particles, such as a hopper, into the transport gas flow.
Particle blasting systems have been around for several decades. Typically, particles, also known as blast media, are fed into a transport gas flow and are transported as entrained particles to a blast nozzle, from which the particles exit, being directed toward a workpiece or other target.
Carbon dioxide blasting systems are well known, and along with various associated component parts, are shown in U.S. Pat. Nos. 4,744,181, 4,843,770, 4,947,592, 5,050,805, 5,018,667, 5,109,636, 5,188,151, 5,301,509, 5,571,335, 5,301,509, 5,473,903, 5,660,580 and 5,795,214, and in commonly owned co-pending applications Ser. No. 09/658,359, filed Sept. 8, 2000, titled Improved Hopper and Ser. No. 09/369,797, filed Aug. 6, 1999, titled Non-Metallic Particle Blasting Nozzle With Static Field Dissipation, all of which are incorporated herein by reference. Many prior art blasting system, such as disclosed therein, include rotating rotors with cavities or pockets for transporting pellets into the transport gas flow. Seals are used in contact with the rotor surface in which the cavities or pockets are formed. Such seals are usually urged against the rotor surface independent of whether the rotor is rotating or the system is operating. The seal force results in seal drag, creating a resisting torque which has to be overcome by the motor. When the torque is present at the time the rotor is started turning, a substantial start up load is placed on the motor, affecting the size and wear of the motor. The prior art large diameter rotors also provide a sizable moment arm through which the seal drag produces substantial torque.
At least for prior art rotors which utilize pockets formed in a peripheral rotor surface, not all pellets are discharged from the pockets at the discharge station. Additionally, the pocket spacing and lack of thorough, uniform mixing of the transport gas and pellets in the feeder results in pulses.
Although the present invention will be described herein in connection with a particle feeder for use with carbon dioxide blasting, it will be understood that the present invention is not limited in use or application to carbon dioxide blasting. The teachings of the present invention may be used in application in which there can be compaction or agglomeration of any type of particle blast media.
Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.